This invention relates to plotters of the type where a pen or other drawing instrument is movable in X and Y coordinate directions relative to a surface supporting a sheet of paper or other sheet material to draw figures, characters and other graphics on the sheet material; and deals more particularly with improvements in such a plotter particularly suited to producing drawings of great length on elongated webs of sheet material, such a drawing being drawn progressively from one of its ends to the other in conjunction with movement of the material over the support surface in one direction parallel to its length.
The plotter of the invention is useful, for example, in the garment industry for drawing markers showing pattern pieces to be cut from a length of fabric. In such application the plotter may be part of a computer assisted pattern grading and marker making system as shown, for example, by U.S. Pat. No. 3,887,903. In this case the sheet material on which the drawing or marker is made is usually paper and the writing instrument is usually a pen. Therefore, for convenience, in the following description and in the accompanying drawings the sheet material is referred to and shown as paper and the writing instrument is referred to and shown as a pen. Other sheet materials and writing instruments may however be used without departing from the invention. It is indeed within the purview of the invention that the plotter may be implemented as a photoplotter with the material on which the drawing is made being a photosensitive sheet or film and with the writing instrument being a beam of light moved over the sheet or film in a line drawing manner to expose lines on the sheet.
As used herein the term "progressive plotter with unidirectional paper movement" refers to a plotter, as suggested above, where a drawing of great length is produced by a pen movable in X and Y coordinate directions over and relative to the plotting area of a paper support surface with the plotting area having only a short dimension parallel to the length of the paper in comparison to the length of drawings to be drawn, with the paper being moved lengthwise in one direction over the plotting area as a drawing is created progressively along its length. A progressive plotter may operate with intermittent paper movement alternating with intermittent plotting, with continuous paper movement combined with continuous plotting, or with a combination of the first two possibilities.
In the first case the plotter may be referred to as a sectional (or section-by-section) plotter characterized in that a drawing to be drawn is divided into a number of sections arranged next to one another lengthwise of the drawing and is created by drawing it one section at a time. That is, the paper is arranged to present one section of it to the plotting area of the plotter, the paper is held stationary relative to the plotting area and the pen of the plotter is then moved in X and Y coordinate directions relative to the plotting area to draw a section of the intended drawing on the section of paper then at the plotting area. After this section of the drawing is completed the paper is advanced lengthwise to bring a next section of paper to the plotting area and the paper is again then held stationary and the pen moved in the X and Y corrdinate directions to draw the next section of the drawing on the section of paper than at the plotting area. This process is repeated section by section until the drawing is finished.
In the second case mentioned above the plotter is operated to draw on the paper, by movement of the pen in X and Y coordinate directions over the plotting area, while the paper is moved over the plotting area continuously in one direction along its length. This means that if at a given point along the length of the drawing a number of lines extend generally lengthwise of the drawing it may be necessary for the pen to draw some or all of such lines in parts, drawing first part of one line, then skipping to another line to draw part of it, and then later returning to the first line to draw another part of it.
In the third case mentioned above the plotter may be operated basically as a sectional plotter to draw most of a drawing one section at a time with the paper being intermittently advanced over the plotting area, but it is also operated so that the pen does some further drawing as the paper is advanced to bring a new paper section to the plotting area. For example, during a paper advancement the pen may be used to draw part of a longitudinally extending border line or to draw all or part of one or more other lines of the basic drawing.
It is presently thought that the plotter of this invention will most often be used for section-by-section drawing, so for convenience it is usually described hereinafter as operating in that way. However, there is no intention to limit the invention to such operation and it is to be understood that the plotter may also be used in other progressive drawing ways without departing from at least the broader aspects of the invention.
Progressive plotters operating in section-by-section fashion are known in the art and are shown, for instance, by U.S. Pat. No. 4,091,980 and U.S. Pat. No. 4,400,704. Such plotters, however, tend to be relatively expensive and to be of relatively massive construction. In particular, the moving parts, especially the X and Y carriages, are large and heavy, the plotter being accordingly either slow in operation or equipped with large and powerful drive motors and very robust associated mechanical drive systems. At least one of the carriages is also quite long and should be made of a heavy rigid construction and to be well supported to avoid vibrations and other deflections leading to drawing errors.
An important requirements of progressive plotters is that the paper track accurately over the plotting area so that in the case of lines necessarily made up of parts drawn at different times with the paper differently positioned relative to the plotting area, the trailing end of one part will coincide exactly with the leading end of the next part to show no discontinuities in a finished complete line. If the paper drifts laterally as it is advanced, or if it buckles or otherwise distorts during the advancement, unacceptable misregistration of line parts, or other drawing errors, are likely to occur.
In the garment industry a need exits for an inexpensive plotter capable of producing, with reasonable speed, accurate long drawings or markers, such need not adequately being filled by presently available and known plotters.
The general object of this invention is therefore to provide an X,Y plotter capable of being made at relatively low cost and which nevertheless is operable to produce long drawings at good speed with a finished complete drawing being very presentable and free of errors such as discontinuities in what should be smooth uninterrupted lines.
A further object of the invention is to provide an X,Y plotter of the foregoing character wherein the plotter is a progressive one with unidirectional paper movement, the arrangement of its parts being such that the moving parts, particularly the X and Y carriages, may be made of relatively small size allowing them to have sufficient rigidity to inhibit vibrations and other deflections while nevertheless being kept light in weight, thereby further allowing them to be driven at acceptably high accelerations and decelerations by relatively low powered inexpensive motors and lightweight drive systems. In keeping with this object of the invention, the arrangement of parts is particularly such that the elongated one of the two carriages does not straddle the width of the paper; the length or the elongated carriage is therefore not dependent on the paper width and is instead of a length significantly, preferably several times, less than the paper width.
A further object of the invention is to provide a plotter of the foregoing character being a paper support and advancement system causing the paper to be advanced over the plotting area in such way as to resist or inhibit various paper tracking problems such as lateral shift, buckling, tearing or other distortion of the paper, or undershoot or overshoot of the paper as it is stopped at the end of any given advancement, such problem-free tracking of the paper assuring proper matching of line parts with one another.
Other objects and advantages of the invention will be apparent from the following description of a preferred embodiment and from the accompanying drawings and claims.